function showpages(){



    //每页显示的数目

    var show_per_page = 2;

    //获取content对象里面，数据的数量

    var number_of_items = $('#content').children().size();

    //计算页面显示的数量

    var number_of_pages = Math.ceil(number_of_items/show_per_page);


    //隐藏域默认值

    $('#current_page').val(0);

    $('#show_per_page').val(show_per_page);



    var navigation_html = '<a class="previous_link" href="javascript:previous();">上一页</a>';

    var current_link = 0;

    while(number_of_pages > current_link){

        navigation_html += '<a class="page_link" href="javascript:go_to_page(' + current_link +')" longdesc="' + current_link +'">'+ (current_link + 1) +'</a>';

        current_link++;
    }


navigation_html += '<a class="next_link" href="javascript:next();">下一页</a>';



    $('#page_navigation').html(navigation_html);



    //add active_page class to the first page link

    $('#page_navigation .page_link:first').addClass('active_page');



    //隐藏该对象下面的所有子元素

    $('#content').children().css('display', 'none');



    //显示第n（show_per_page）元素

    $('#content').children().slice(0, show_per_page).css('display', 'block');



};



//上一页

function previous(){

    new_page = parseInt($('#current_page').val()) - 1;

    //if there is an item before the current active link run the function

    if($('.active_page').prev('.page_link').length==true){

        go_to_page(new_page);

    }



}

//下一页

function next(){

    new_page = parseInt($('#current_page').val()) + 1;

    //if there is an item after the current active link run the function

    if($('.active_page').next('.page_link').length==true){

        go_to_page(new_page);

    }



}

//跳转某一页

function go_to_page(page_num){

    //get the number of items shown per page

    var show_per_page = parseInt($('#show_per_page').val());



    //get the element number where to start the slice from

    start_from = page_num * show_per_page;



    //get the element number where to end the slice

    end_on = start_from + show_per_page;



    //hide all children elements of content div, get specific items and show them

    $('#content').children().css('display', 'none').slice(start_from, end_on).css('display', 'block');



    /*get the page link that has longdesc attribute of the current page and add active_page class to it

     and remove that class from previously active page link*/

    $('.page_link[longdesc=' + page_num +']').addClass('active_page').siblings('.active_page').removeClass('active_page');



    //update the current page input field

    $('#current_page').val(page_num);

}

